Chronology and Genesis of S-type Granites in Hetai District, Guangdong Province: Constraints from LA-ICP-MS Zircon U-Pb Dating and Tourmaline Boron Isotope In-situ Analyses

1 Introduction Hetai district,which is a mountainous area,situated on Guangning and Zhaoqing city,west Guangdong Province.Hetai district is generally located on southwest of South China Caledonian fold belt,east margin of Yunkai post-Caledonian uplift.Multiple type granites are widely distributed in Hetai district,including Caledonian,Indosinian and Yanshanian granites.Based on different

LA-ICP-MS Zircon U-Pb Dating of Intermediate-Acidic Intrusive Rocks and Molybdenite Re-Os Dating from the Bangpu Mo (Cu) Deposit, Tibet and its Geological Implication

The multi-stage intrusions of intermediate-acid magma occur in the Bangpu mining district, the petrogenic ages of which have been identified. The times and sequences of their emplacement have been collated and stipulated in detail in this paper by using the laser ablation-inductively coupled plasma-mass spectrometry （LA-ICP-MS） zircon U-Pb dating method. The ages of biotite monzogranite that were formed before mineralization in the southwest of this mining district are 70±1 Ma （mean square of weighted deviates （MSWD） =9.5, n=8） and 60.60±0.31 Ma （MSWD=3.8, n=16）, which belong to the late Cretaceous-early Paleocene in age. That means, they are products of an early tectonicmagmatic event of the collision between the Indian and Asian continentals. The ages of ore-bearing monzogranite porphyry and ore-bearing diorite porphyrite are 16.23±0.19 Ma （MSWD=2.0, n=26） and 15.16±0.09 Ma （MSWD=3.9, n=5） separately, which belong to the middle Miocene in age; namely, they are products of the Gangdese post-collision extensional stage when crust-mantle materials melted and mixed as well as magmatic intrusion simultaneously occurred. Some zircons with ages of 203.6±2.2 Ma （MSWD=1.18, n=7） were captured in the ore-bearing diorite porphyrite, which shows that there had been tectono-magmatic events in the late Triassic-early Jurassic. Molybdenum （copper） ore-bodies produced in the monzogranite porphyry and copper （molybdenum） ore-bodies produced in the diorite porphyrite are the main ore types in this ore deposit. The model ages of Re-Os isotopic dating for the 11 molybdenite are 13.97-15.84 Ma, while isochron ages are 14.09±0.49 Ma （MSWD=26）. The isochron ages of seven molybdenite from molybdenum （copper） ore with monzogranite porphyry type are 14.11±0.31 Ma （MSWD=5.2）. There is great error in the isochron ages of four molybdenite from copper （molybdenum） ore with diorite porphyrite type, and their weighted average model ages of 14.6±1.2 Ma （MSWD=41）, which generally represent the mineralization age. The results about the Re-Os isotopic dating of molybdenite in the ore of different types have limited exactly that, the minerlazation age of this ore deposits is about 14.09 Ma, which belongs to the middle Miocene mineralization. The Bangpu deposit has a uniform metallogenic dynamics background with the porphyry type and skarn-type deposits such as Jiama, Qulong and others.

Geochemical Characteristics and LA-ICP-MS Zircon U-Pb Dating of Amphibolites in the Songshugou Ophiolite in the Eastern Qinling

Geochemical studies on the arnphibolites in the Songshugou ophiolite from Shangnan County, Shaanxi Province demonstrate that the protolith of the amphibolites is tholeiitic. The arnphibolites can be classified into two groups according to their REE patterns and trace element features. Rocks of the first group are depleted in LREE while rocks of the second group are slightly depleted in LREE or flat from LREE to HREE without significant Eu anomaly. The first group of rocks have (La/Yb)N=0.33-0.55, (La/Sm)N= 0.45-0.65, and their La/Nb, Ce/Zr, Zr/Nb, Zr/Y and Ti/Y ratios are averaged at 1.20, 0.12, 31.02, 2.92 and 198, respectively, close to those of typical N-MORB. The second group of rocks have (La/Yb)N=0.63-0.95, (La/ Sm)N = 0.69--0.90, and their average La/Nb, Ce/Zr, Zr/Nb, Zr/Y and Ti/Y ratios are 0.82, 0.83, 1.15, 0.16, 19.00, 2.58 and 225, respectively, which lie between those of typical N-MORB and E-MORB but closer to the former. The two groups of rocks both exhibit flat patterns from Th to Yb in the highly incompatible elements spider diagram, but the first group of rocks have lower element abundances than the modern N-MORB, indicating a derivation of their mantle source from more depleted mantle source than the present N-MORB. The abundances of Th, Ta, Nb, La and Ce in the second group of rocks are slightly higher than those of the present N-MORB, and other elements, such as Hf, Zr, Sm, Ti, Y and Yb, are close to those of the N-MORB, indicating that the original magma was derived from depleted mantle but mixed with the enriched mantle. These characteristics, combined with the regional geology and previous studies, provide further evidence that the mafic-ultramafic rocks have the features of a typical ophiolite.Zircon grains from the amphibolite are generally rounded, and in most of them a distinguishable core-mantle texture is preserved as shown in the cathodoluminescence (CL) images. The core or core-mantle parts of the zircon grains are also rounded, same as those in basalts from other regions of the world. The LA-ICP-MS trace element and U-Pb isotopic analyses show that the zircon grains from the amphibolites are similar to the typical magmatic zircon in terms of their very low U and Th contents (62.36-0.10 μg/g and 78.47-0.003 μg/g, respectively). Seven pits from the core and core-mantle parts of the zircon grains yielded an average weighted 206Pb/ 238U age of 973±35 (2σ) Ma with the Th/U ratios range from 0.01 to 8.38 and mostly greater than 0.23. This age is consistent within the error range with the whole-rock Sm-Nd isochron age of 1030±46 Ma for the same kind of rocks reported by Dong et al. (1997a). In a combined analysis with the zircon positions on the CL images and the corresponding Th/U ratios, the age of 973±35 Ma is probably the formation age of tholeiite, the protolith of the Songshugou amphibolite. The geochronological determination gives further evidence that the Songshugou ophiolite was formed during the Neoproterozoic. In addition, there is one pit from the rim of a zircon grain giving a 206Pb/ 238U age of 5721199 (1σ) Ma with a Th/U ratio of 0.08. It may represent the age of the accretionary zircon in the amphibolite-facies metamorphism.

LA-ICP-MS Zircon U-Pb Geochronology of the Fine-grained Granite and Molybdenite Re-Os Dating in the Wurinitu Molybdenum Deposit,Inner Mongolia,China

The Wurinitu molybdenum deposit,located in Honggor,Sonid Left Banner of Inner Mongolia,China,is recently discovered and is considered to be associated with a concealed fine-grained granite impregnated with molybdenite.The wall rocks are composed of Variscan porphyritic-like biotite granite and the Lower Ordovician Wubin'aobao Formation.LA-ICP-MS zircon U-Pb dating of the fine-grained granite reveals two stages of zircons,one were formed at 181.7±7.4 Ma and the other at 133.6±3.3 Ma.The latter age is believed to be the formation age of the fine-grained granite,while the former may reflect the age of inherited zircons,based on the morphological study of the zircon and regional geological setting.The Re-Os model age of molybdenite is 142.2±2.5 Ma,which is older than the diagenetic age of the fine-grained granite.Therefore the authors believe that the metallogenic age of the Wurinitu molybdenum deposit should be nearly 133.6±3.3 Ma or slightly later,i.e.,Early Cretaceous.Combined with regional geological background research,it is speculated that the molybdenum deposits were formed at the late Yanshanian orogenic cycle in the Hingganling-Mongolian orogenic belt,belonging to the relaxation epoch posterior to the compression and was associated with the closure of the Mongolia-Okhotsk Sea.

Single Zircon LA-ICP-MS U-Pb Dating of the Guandimiao and Wawutang Granitic Plutons in Hunan,South China and Its Petrogenetic Significance

The Guandimao and Wawutang plutons are located at the center of Hunan, South China. The former is mainly composed of biotite monzonitic granites/granodiorites and two-mica monzonltic granites, but the latter only consists of biotite monzonitic granites. The zircon ages of 203.0±1.6 Ma （biotite monzonitic granites） and 208.0-23.2 Ma （two-mica monzonltic granites） for the Guandimao pluton and 204±3 Ma for the Wawutang pluton obtained with the LA-ICP-MS U-Pb dating indicate that they were formed during the late Indosinian. In consideration of other geochronological data from Indosinian rocks of South China and adjacent regions, it is inferred that the two plutons were derived from crustal materials by decompressional melting in a post-collisional tectonic setting during spontaneous thinning of the thickened curst. Moreover, the inherited zircon age of 1273±57 Ma from the Wawutang pluton indicates that the source of the two plutons is related to the early Proterozoic crustal basement.

LA-ICP-MS U-Pb Zircon Dating for Felsic Granulite, Huangtuling Area, North Dabieshan: Constraints on Timing of Its Protolith and Granulite-Facies Metamorphism, and Thermal Events in Its Provenance

Information about the protolith of the Huangtuling granulite in North Dabieshan has been unavailable. The complex evolution history of the rock and its host basement must be further discussed. LA-ICP-MS U-Pb dating was conducted on three textural domains in zircon from a high-temperature, high-pressure felsic granulite in the Huangtuling area, North Dabieshan, Central China. The metamorphic growth-derived detrital zircon domain yields a 207^ pb/206^Pb age in the range of （2 49±54 ） -- （2 500±180） Ma. The magmatic genesis-derived detrltal zircon domain gives a 207^pb/ 206^Pb age ranging from 2 628 Ma to 2 690 Ma, with an oldest 206^ pb/ 238^U age of （2 790 ± 150） Ma. The metamorphic overgrowth or metamorphic recrystallization zircon domain yields a diesordia with an upper intercept age of （2 044. 7 ± 29.3 ） Ma. Compositions of the mineral assemblage, major element geochemistry, and especially the complex interior texture of the zircon suggest that the prololith of the felsic granulite is of sedimentary origin. Results show that the protolith material of the granulite came from a provenance with a complex thermal history, i.e. -2.8 Ga magmatlsm and -2.5 Ga metamorphism, and was deposited in a basin not earlier than 2.5 Ga. The high-temperature and high-pressure granulite-facies metamorphic age was precisely constrained at （2.04±0.03） Ga, which indicates the granulite in Huangtuling area should be a relict of a Paleoproterozoic UHT （ultrahigh temperature） metamorphosed slab.

Types and Correction Methods of Matrix Effect during Zircon LA-ICP-MS U-Pb Dating

Matrix effect primarily impacts the accuracy and precision of zircon LA-ICP-MS U-Pb data.This paper describes three types of matrix effect in zircon LA-ICPMS U-Pb dating,i.e.,the element matrix effect,high Ddpa or uranium matrix effect and alpha dose matrix effect,and illustrates the correction of these three effects.In addition,we point out the limitation and possible problems of the existing correction methods.

Geochemistry and Zircon LA-ICP-MS U-Pb Dating for the Ganlongtang-Longba Ophiolite,Changning-Menglian Suture Zone

The detailed geochemical research indicates that the tholeiitic basalts from Ganlongtang-Longba ophiolitic m（?）lange exhibit distinctive geochemical characteristics of high TiO2 and low K2O,and depletion of light rare earth elements.They should be originated from a depleted asthenosphere mantle, belonging to ancient oceanic crust ophiolitic volcanic rock association.Compared with the Longba tholeiitic basalt,the Ganlongtang tholeiitic basalt shows

Mesozoic Bimodal Volcanic Suite in Zhalantun of the Da Hinggan Range and Its Geological Significance: Zircon U-Pb Age and Hf Isotopic Constraints

Mesozoic bimodal volcanic rocks of basaltic andesite and rhyolite are widely distributed in the Da Hinggan Range, but their petrogenetic relationships and geodynamic implications are rarely constrained. Detailed studies on doleritic and porphyry dikes in the Zhalantun area indicate that they display features of magma mixing, suggesting their coeval formation. In situ zircon U-Pb dating shows that the porphyry was emplaced in the Early Cretaceous with a ^206Pb/^238U age of 130±1 Ma. Zircons from the dolerite also yield an Early Cretaceous emplacement age of 124±2 Ma although some inherited zircons have been identified. These age results indicate that the Early Cretaceous was an important period of magmatism in the Da Hinggan Range. Zircons from porphyry are characterized by positive value of εHf（t） as high as 10.3±0.5 with Hf depleted mantle model age of 349-568 Ma, whereas magmatic zircons from the dolerite have εHf（t） value of 11.0±1.4 with Hf depleted mantel model age of 342-657 Ma, consistent with those from the porphyry. Considering other data on the geological evolution of this area, it is concluded that the mafic magma originated from the partial melting of Paleozoic enriched lithospheric mantle, whereas the felsic magma came from recycling of juvenile crust formed during the Paleozoic. Both of the protoliths are closely related to the subduction of the Paleo-Asian Ocean during the Paleozoic, indicating that the Paleozoic is an important period of large-scale crustal growth in the area.

Zircon LA-ICP MS U-Pb Age,Sr-Nd-Pb Isotopic Compositions and Geochemistry of the Triassic Post-collisional Wulong Adakitic Granodiorite in the South Qinling,Central China,and Its Petrogenesis

The Indosinian post-collisional Wulong pluton intruded into the Mesoproterozoic Fuping Group, South Qinling, central China. In the southern part of the pluton, some mafic enclaves have sharp or gradational contact relationships with the host biotite granodiorite. Geochemistry, zircon LA-ICP MS （laser ablation inductively-coupled plasma mass spectrometry） U-Pb chronology and Sr- Nd-Pb isotope geochemistry of the pluton are reported in this paper. The biotite granodiorite shows close compositional similarities to high-silica adakite. Its chondrite-normalized REE patterns are characterized by strong HREE depletion （Yb = 0.33--0.96 10-6 and Y = 4.77-11.19 ×10^-6）, enrichment of Ba （775-1386 x 10-6） and Sr （643-1115 × 10^-6） and high Sr/Y （57.83-159.99） and Y/Yb （10.99-14.32） ratios, as well as insignificant Eu anomalies （6Eu = 0.70-0.83）, suggesting a feldspar-poor, garnet±amphibole-rich residual mineral assemblage. The mafic enclaves have higher MgO （4.15- 8.13%）, Cr （14.79-371.31 × 10-6）, Ni （20.00-224.24× 10^-6） and Nb/Ta （15.42-21.91） than the host granodiorite, implying that they are mantle-derived and might represent underplated mafic magma. Zircon LA-ICP MS dating of the granodiorite yields a ^206pb/^238U weighted mean age of 208±2 Ma （MSWD=0.50, 1σ）, which is the age of emplacement of the host biotite granodiorite. This age indicates that the Wulong pluton formed during the late-orogenic or post-collisional stage （〈242±21 Ma） of the South Qinling belt. The host biotite granodiorite displays ^87Sr/^86Sr = 0.7059-0.7062, Isr = 0.7044-- 0.7050,^143Nd/^144Nd = 0.51236-0.51238, εNd（t）= -2.26 to -2.66 to ^206Pb/^204pb = 18.099-18.209, ^207pb/^204pb = 15.873-15.979 and ^208pb/^204pb = 38.973-39.430. Those ratios are similar to those of the Mesoproterozoic Yaolinghe Group in the South Qinling. Furthermore, its Nd isotopic model age （-1.02 Ga） is consistent with the age （-1.1 Ga） of the Yaolinghe Group. Based on the integrated geological and geochemical studies, coupled with previous studies, the authors suggest that the Wulong adakitic biotite granodiorite was probably generated by dehydration melting of the Yaolinghe Group-like thickened mafic crust, triggered by underplating of mafic magma at the boundary of the thickened mafic crust and hot lithospheric mantle, and that the Wulong adakitic biotite granodiorite may have resulted from thinning and delamination of the lower crust or breakoff of the subducting slab of the Mianlue ocean during the Indosinian post-collisional orogenic stage of the Qinling orogenic belt.

Ages of the Laocheng Granitoids and Crustal Growth in the South Qinling Tectonic Domain,Central China:Zircon U-Pb and Lu-Hf Isotopic Constraints

The Laocheng granitoid pluton is located in the South Qinling tectonic domain of the Qinling orogenic belt,southern Shaanxi Province,and consists chiefly of quartz diorite,granodiorite and monzogranite.A LA-ICP-MS zircon U-Pb isotopic dating,in conjunction with cathodoluminescence images,reveals that the quartz diorite and granodiorite were emplaced from 220 Ma to 216 Ma,while the monzogranite was emplaced at～210 Ma.In-situ zircon Hf isotopic analyses show that theε_（Hf）（t） values of the quartz diorite and granodiorite range from-8.1 to ＋1.3,and single-stage Hf model ages from 809 Ma to 1171 Ma,while theε_（Hf）（t）values of the monzogranite are-14.5 to ＋16.7 and single-stage Hf model ages from 189 Ma to 1424 Ma.These Hf isotopic features reveal that the quartz diorite, granodiorite and monzogranite were formed from the mixing of the magmas derived from partial melting of the depleted mantle and the lower continent crustal materials,and there were two stages of continental crust growth during the Neoproterozoic（～800 Ma）and Indosinian（～210 Ma）eras, respectively,in the south Qinling tectonic domain of the Qinling orogrnic belt,Central China.

Zircon U-Pb Geochronology and Hf Isotopic Constraints on Petrogenesis of Plagiogranite from the Cuomuqu Ophiolite,Bangong Lake Area,North Tibet

Field observation, geochemical signatures and zircon Hf isotope data indicate that Cuomuqu ophiolite in the Bangonghu area was formed in a back-arc basin （BAB） above a supra- subduction zone （SSZ）. Zircon U-Pb dating of the diabase from the Cuomuqu massif yielded an age of 164.3±1.9 Ma, thus indicating that the ophiolite complex was formed in the Middle Jurassic during back-arc extension of the mature Bangonghu-Nujiang Ocean. The zircon εHf（t） and TDMC values of the plagiogranite are similar to the εHf（t） and TDM of the diabase, respectively. The mode of occurrence of plagiogranites and their bulk-rock and Hf isotope characteristics indicate that they were derived from the mantle, associated with the surrounding gabbro and diabase, and were formed by partial melting of altered and hydrated mafic rocks under shear conditions during lateral drifting of the oceanic crust. The zircon U-Pb age of the plagiogranite is 156.4±1.4 Ma, and it is 7.9 Ma younger than the hosting diabase. In this study, zircon chronological and Hf isotopic data were tentatively analyzed to determine the genesis of plagiogranites in the Cuomuqu ophiolite complex.

Precambrian Tectonic Affinity of the Southern Langshan Area, Northeastern Margin of the Alxa Block: Evidence from Zircon U-Pb Dating and Lu-Hf Isotopes

The Alxa Block is the westernmost part of the North China Craton(NCC), and is regarded as one of the basement components of the NCC. Its geological evolution is of great significance for the understanding of the NCC.However, the Precambrian basement of the Alxa Block is still poorly studied. In this study, we present new in situ LA-ICPMS zircon U-Pb and Lu-Hf isotope data from the Diebusige Metamorphic Complex(DMC) which located in the eastern Alxa Block. Field and petrological studies show that the DMC consists mainly of metamorphic supracrustal rocks and minor metamorphic plutonic rocks and has experienced amphibolite-granulite facies metamorphism. Zircon U-Pb dating results suggested that the amphibolite sample yields a crystallization age of 2636 ± 14 Ma and metamorphic ages of 2517–2454 Ma and 1988–1952 Ma, proving the existence of exposed Archean rocks in the Langshan area and indicating that late Neoarchean to Paleoproterozoic metamorphic events existed in the Alxa Block. Two paragneiss samples show that the magmatic detrital zircons from the DMC yield 207Pb/206Pb ages ranging from 2.48 Ga to 2.10 Ga with two youngest peaks at 2.13 Ga and 2.16 Ga, respectively, and they were also overprinted by metamorphic events at 1.97–1.90 Ga and 1.89–1.79Ga. Compilation of U-Pb ages of magmatic detrital and metamorphic zircons suggested that the main part of the DMC may have been formed at 2.1–2.0 Ga. Zircon Lu-Hf isotope data show that the source materials of the main part of the DMC were originated from the reworking of ancient Archean crust(3.45–2.78 Ga). The Hf isotope characteristics and the tectonothermal event records exhibit different evolution history with the Khondalite Belt and the Yinshan Block and the other basements of the Alxa Block, indicating that the Langshan was likely an independent terrain before the middle Paleoproterozoic and was subjected to the middle to late Paleoproterozoic tectonothermal events with the Khondalite Belt as a whole.

Late Paleozoic Mantle Source Nature of Tianshan Orogen, Northwest China: Evidence from the Geochemistry, Zircon U-Pb Dating, Hf and Whole Rock Sr-Nd-Pb Isotopes of the Mafic Dykes

The Tianshan Orogen(TO)is one of the largest typical accretionary orogenic belts in the world.Of which,the late Paleozoic was a critical era to understand the tectonic and geodynamic transition from accretion to collision.However,the late Paleozoic tectonic evolutionary history,especially for the time of the ocean-continent transition,is still debated although the origin and tectonic settings for the Paleozoic volcanic,felsic igneous magmatism in TO and reginal geology have been done in the last decades.In contrast,the researches on the mafic dykes in TO was not systematically carried out till now.Reginal-scale mafic dykes are commonly regarded as the products created in a extensional setting,and used to identify the major tectonic events such as rifting and continental break-up and further trace the mantle natures and geodynamic mechanism(Halls,1982;Bleeker and Ernst,2006;Li et al.,2008;Ernst et al.,2010;Srivastava,2011;Hou,2012;Peng,2015;Peng et al.,2019).There are widespread late Paleozoic mafic dykes beside the huge of intermediate-acid igneous rocks in the TO,being an idea object to reveal the extensional events,tectonic evolution and the mantle nature and geodynamic processes.We present the ICPMS in situ zircon U–Pb dating,Lu-Hf and whole-rock Sr-Nd isotopes as well as the geochemistry data for these mafic dykes to better constraint their petrogenesis and mantle nature.New zircon U-Pb dating for 12 samples from the representative basic dykes and basalts yield three distinct stages of^332 Ma,316–302 Ma and 288–282 Ma,respectively.In which,the first stage of mafic dykes is mainly occurred in both East Tianshan Orogen(ETO)and West Tianshan Orogen(WTO),and composed of dolerite with minor basalts.The second stage of mafic dyke also can be found in both ETO and WTO.However,in contrast to the first stage of mafic dykes,they have relatively variable rock types from the dolerite/or gabbros to gabbroic diorite.The third stage of mafic dykes are slightly intermediate in composition,and chiefly consist of andesitic-basaltic dolerite with some diorites.They are widely developed not only in both ETO and WTO,but also in the Beishan area to the east of the ETO,indicating a large-scale mafic magmatism in Tianshan and adjacent areas.

A ca. 2.2Ga Acidic Magmatic Event at the Northern Margin of the Yangtze Craton: Evidence from U-Pb Dating and Hf Isotope Analysis of Zircons from the Kongling Complex

Objective The Yangtze craton collisional orogeny at ca. extensional events at ca. 1 experienced Paleoproterozoic 1.95-2.0 Ga and post-orogenic 85 Ga related to amalgamation of the Columbia （Nuna） supercontinent （Zhao and Cawood, 2012）. A ca. 2.15 Ga suprasubduction zone ophiolitic melange was recongized in the Archean- Paleoproterozoic Kongling Complex of the northern Yangtze craton （Han et al., 2017）. However, the tectonic evolution in early Paleoproterozoic from 2.4 Ga to 2.2 Ga remains unclear. We report here the presence of a suite of Paleoproterozoic （2.2 Ga） granites in the Huangling dome, northern Yangtze craton, which may provide important insights into crustal growth processes in the craton prior to the assembly of Columbia.

Geochemistry, Zircon U–Pb Dating and Hf Isotopic Characteristics of Neoproterozoic Granitoids in the Yaganbuyang Area, Altyn Tagh, NW China

The South Altyn continental block is an important geological unit of the Altyn Tagh orogenic belt, in which numerous Neoproterozoic granitoids crop out. Granitoids are mainly located in the Paxialayidang-Yaganbuyang area and can provide indispensable information on the dynamics of Rodinia supercontinent aggregation during the Neoproterozoic. Therefore, the study of granitoids can help us understand the formation and evolutionary history of the Altyn Tagh orogenic belt. In this work, we investigated the Yaganbuyang granitic pluton through petrography, geochemistry, zircon U-Pb chronology, and Hf isotope approaches. We obtained the following conclusions： （1） Yaganbuyang granitoids mainly consist of two-mica granite and granodiorite. Geochemical data suggested that these granitoids are peraluminous calc-alkaline or high-K calc-alkaline granite types. Zircon U-Pb data yielded ages of 939~7.1 Ma for granodiorite and ~954 Ma for granitoids, respectively. （2） The ~Hf（t） values of two--mica granite and granodiorite are in the range of-3.93 to ＋5.30 and -8.64 to ＋5.19, respectively. The Hf model ages （TDM2） of two-mica granite and granodiorite range from 1.59-.05 Ga and 1.62-2.35 Ga, respectively, indicating that the parental magma of these materials is derived from ancient crust with a portion of juvenUe crust. （3） Granitoids formed in a collisional orogen setting, which may be a response to Rodinia supercontinent convergence during the Neoproterozoic.

Petrogenesis of the Xihuashan Granite in Southern Jiangxi Province,South China:Constraints from Zircon U-Pb Geochronology,Geochemistry and Nd Isotopes

Mesozoic granitic intrusions are widely distributed in the Nanling region, South China. Yanshanian granites are closely connected with the formation of tungsten deposits. The Xihuashan granite is a typical representative of tungsten-bearing granite. The Xihuashan granite consists mainly of medium-grained porphyritic biotite granite, medium-grained biotite granite and fine-grained twomica granite, which correspond to LA-ICP-MS zircon U-Pb ages of 555.5±0.4 Ma, 553.0±0.6 Ma and 552.8±0.9 Ma, respectively. Rocks from the Xihuashan mining area displays high SlOe （73.85% to 76.49%） and NaeO＋K20 contents （8.09% to 9.43%）, belonging to high-K calc-alkaline series. They are metaluminous to weakly peraluminous with A/CNK values ranging from 0.96 to 5.06. All granites in this study area are rich in Rb, Th, U and Pb, and depleted in Ba, Sr, P, Ti, Nb and Eu, especially depleted in medium-grained biotite granite and fine-grained two-mica granite. The medium-grained porphyritic biotite granites usually have high LREE concentrations, whereas medium-grained biotite granite and fine-grained two-mica granite displays high HREE contents. Our geochemical data reveal that the studied rocks are highly fractionated I-type granite. The magma underwent strong magma differentiation with decreasing temperature and increasing oxygen fugacity, which may explain the formation of three types of distinct granites. Variations of Rb, Sr and Ba concentrations in different type granites were controlled by fractional crystallization of biotite and feldspar. Fractional crystallization of monazite, allanite and apatite resulted in LREE changes in granite, and formation of garnet mainly caused HREE changes. Granites from the Xihuashan mining area have relatively high εd（t） values （-9.77 to -55.46）, indicating that they were probably generated by partial melting of underlying Proterozoic metasedimentary rocks with minor addition of juvenile crust or mantlederived magmas.

Geochemistry,Geochronology,Sr-Nd Isotopic Compositions of Jiang Tso Ophiolite in the Middle Segment of the Bangong- Nujiang Suture Zone and Their Geological Significance

The Jiang Tso ophiolite, situated in the middle segment of the Bangong- Nujiang Suture Zone, is a part of the easternmost Qieli Lake ophiolite subzone and is close to the south of Pung Lake ophiolite. The rock association of Jiang Tso ophiolite is relatively complete and is mainly composed of metamorphic peridotite, gabbro and diabase. Comparing with N-MORB, the ophiolite is high in Mg and low in Ti, K, Na, P, and is depleted in Nb, Ta, Hf, Th and enriched in Rb, Sr and Ba. Geochemical characteristics of the Jiang Tso ophiolite indicate it is of a supra-subduction zone type formed in the spreading ridge of back arc basin. The SHRIMP U-Pb dating of zircons from the gabbro yielded a weighted average age of 188.1±4.1 Ma （MSWD=1.4）, indicating the Jiang Tso ophiolite was formed in the late stage of early Jurassic. The Sr, Nd isotopic compositions show that the Tethyan mantle domain is the depleted mantle （DM）, with enriched mantle domain II （EMII）. They have the same Sr, Nd isotopic composition with the India Ocean MORB type.

Geochronology,Fluid Inclusions and Isotopic Characteristics of the Dongjun Pb-Zn-Ag Deposit,Inner Mongolia,NE China

The Dongjun Pb-Zn-Ag deposit in the northern part of the Great Xing’an Range(NE China)consists of quartzsulfide vein-type and breccia-type mineralization,related to granite porphyry.Hydrothermal alteration is well-developed and includes potassic-silicic-sericitic alteration,phyllic alteration and propylitic alteration.Three stages of mineralization are recognized on the basis of field evidence and petrographic observation,demarcated by assemblages of quartz-pyritearsenopyrite(early stage),quartz-polymetallic sulfide(intermediate stage)and quartz-carbonate-pyrite(late stage).Zircon LA-ICP-MS U-Pb dating indicates that the granite porphyry was emplaced at 146.7±1.2 Ma(Late Jurassic).Microthermometry and laser Raman spectroscopy shows that ore minerals were deposited in conditions of intermediate temperatures(175-359℃),low salinity(0.5-9.3 wt% Na Cl eqv.)and low density(0.60-0.91 g/cm^(3)).Ore-forming fluids were derived largely from magmatic hydrothermal processes,with late-stage addition of meteoric water,belonging to a H_(2)O-NaCl-CO_(2)±CH_(4) system.The δ^(34)SV-CDT values range from 0.75‰ to 4.70‰.The ^(206)Pb/^(204)Pb,^(207)Pb/^(204)Pb,and ^(208)Pb/^(204)Pb values of the ore minerals are in the ranges of 18.240-18.371,15.542-15.570,and 38.100-38.178,respectively.Data for the S and Pb isotopic systems indicate that the ore-forming metals and sulfur were derived from Mesozoic magma.Based on the geological characteristics and geochemical signatures documented in this study,we conclude that the Dongjun deposit is a mesothermal magmatic hydrothermal vein-type Pb-Zn-Ag deposit controlled by fractures and related to granite porphyry,in response to Late Jurassic tectonic-magmatic-hydrothermal activity.We further conclude that fluid immiscibility,fluid mixing and fluid-rock interactions were the dominant mechanisms for deposition of the ore-forming materials.

Petrogenesis of Kejie Granite in the Northern Changning-Menglian Zone, Western Yunnan: Constraints from Zircon U-Pb Geochronology, Geochemistry and Hf Isotope

The Kejie pluton is located in the north of the Changning-Menglian suture zone. The rock types are mainly biotite-granite. Zircon LA-ICP-MS U-Pb dating indicates that the Kejie pluton emplaced at about 80-77 Ma, Late Cretaceous. The Kejie pluton samples are characterized by high SiO2 （71.68%-72.47%）, K2O （4.73%-5.54%）, total alkali （K2O ＋ Na2O = 8.21%-8.53%）, K2O/Na2O ratios （1.36-1.94） and low P2O5 （0.13%-0.17%）, with A/CNK of 1.025-1.055; enriched in U, Th, and K, depleted in Ba, Nb, St, Ti, P and Eu. They are highly fractionated, slightly peraluminous 1-type granite. The two samples of the Kejie pluton give a large variation of εHf（t） values （-5.04 to 1.96） and Hf isotope crustal model ages of 1.16-1.5 Ga. Zircon Hf isotopes and zircon saturation temperatures of whole-rock （801℃-823℃） show that the mantle-derived materials maybe have played a vital role in the generation of the Kejie pluton. The Kejie pluton was most likely generated in a setting associated with the eastward subduction of the neo-Tethys ocean, where intrusion of mantle wedge basaltic magmas in the crust caused the anatexis of the latter, forming hybrid melts, which subsequently experienced high-degree fractional crystallization.